Ratio and Proportion

Concept:Use the given ratio and the second train's speed to find the first train's speed.Explanation:Speed of the second train = $\frac{400 \text{ km}}{5 \text{ h}} = 80 \text{ km/hr}$.The ratio of speeds (first : second) is $7 : 8$.Let the speed of the first train be $7x$ and the second be $8x$.Since $8x = 80$, solving gives $x = 10$.Thus speed of the first train = $7 \times 10 = 70 \text{ km/hr}$.This value does not match any of the given options (10, 50, 71).Answer:D. None